Homonymous hemianopia (HH) is vision loss in one half of the visual field due to stroke, head trauma or tumor. Strabismus, misalignment of the eyes, is present with HH 10 times more often than expected. Strabismus may compensate for HH if the deviant eye points into the blind hemi- field and if harmonious anomalous retinal correspondence (HARC) has also developed, however there is no data showing whether the compensation gives any advantage to the child who develops both visual impairments. We will conduct a retrospective study of a large population of children who have both strabismus and hemianopia. Previous publications have only examined, at most, four cases, and have not measured any effect of the condition on mobility. We have identified 119 patients who have both impairments at Boston Children's Hospital. Thus, this will be the largest study of its kind and have a positive impact on pediatric healthcare, regardless of outcome. Moreover, it suggests that this combination of visual impairments is not as rare as assumed. Worldwide there may be one hundred thousand children with both visual impairments. We will measure visual functioning in these patients (retinal correspondence and suppression in central and peripheral visual field, binocular vision, diplopia, and visual field extent) and mobility with regards to hazard detection in driving and obstacle avoidance in walking. This will allow us to determine whether strabismus indeed offers any advantage in children with HH. We will also use prism correction to measure the potential effect of strabismus surgery in these participants. To understand the long term effects of strabismus surgery, we will examine the subset of 24 patients in this population who have had strabismus surgery. These participants will be tested to discover whether prism glasses can restore HARC while permitting the benefits of surgery. Such a treatment would allow children to enjoy the benefits of surgery as well as any mobility improvements we observed. It may also allow such patients to pass driving license requirements, which is important in many countries throughout the world.